1. Field of Invention
The present invention relates to monitors for circuit breakers in electrical power distribution systems.
2. Description of Prior Art
It has long been necessary for electrical power utilities to perform routine maintenance tests on power distribution equipment. One type of such equipment on which maintenance has been particularly important from a standpoint of safety and security has been power circuit breakers. These circuit breakers are quite large and very expensive. They operate in multi-phase service conditions where each breaker must carry voltages in ranges as high as several tens of thousands of volts and current levels of several hundred or more amperes.
One established testing procedure was to periodically remove the circuit breaker from active service and verify circuit breaker performance through a series of tests. Examples of such tests were timing, micro-ohm and insulation tests. The information obtained during these out-of-service tests was very useful. However, as has been pointed out, it was necessary to remove the circuit breakers from service to perform these types of tests.
It was a costly process to remove such a power circuit breaker from service for maintenance testing. It was also difficult to schedule the tests because the uncertainty of service demand levels limited equipment availability scheduling. Due to the adverse effect on system power delivery of removal of certain portions of the power distribution equipment from service, scheduled testing often was delayed or even cancelled.
More recently, test equipment has become available to monitor and record functions of the control circuit mechanisms associated with the power circuit breakers without removing the circuit breakers from active service. These control circuit monitors offered the advantage that the circuit breaker did not have to be removed from service for testing. There still remained the drawback that the actual components of the circuit breaker involved in breaking the electrical power circuit were not tested while in actual service. This monitoring and recording test equipment did, at least, provide certain information by monitoring electrical signals in the control circuits associated with the power circuit breakers.
Situations have still, though, been known to be likely to occur where the electrical control circuitry of the breakers was performing satisfactorily and the circuit breaker thus would be deemed acceptable. In actuality, it could later develop that although the control circuitry was satisfactory, this was a misleading indication. The actual components of the circuit breaker involved in physically breaking the flow of current were either worn or defective and these shortcomings had gone undetected during control circuitry testing.